1. Field of the Invention
The invention is directed to an improved rotary vane pump.
2. Description of the Prior Art
A vane pump known from DE 199 52 167 A1 has a pump housing that contains a rotor which is driven in rotary fashion by a drive shaft. The rotor has a number of grooves distributed over its circumference that extend at least essentially in the radial direction in relation to the rotation axis of the rotor, in each of which a wing-shaped delivery element is guided in sliding fashion. The pump housing has a circumferential wall surrounding the rotor and arranged eccentrically in relation to its rotation axis, against which the radially outer ends of the wings rest. The pump housing has housing end walls that adjoin the rotor in the direction of its rotation axis. As the rotor rotates, because of the eccentric arrangement of the circumferential wall, expanding and contracting chambers are formed between the wings, between which chambers the medium to be delivered is conveyed by means of a pressure increase from a suction region to a pressure region that is offset from it in the circumferential direction. Due to centrifugal forces, as the rotor rotates, the wings are kept in contact with the circumferential wall; but particularly when the vane pump is starting up, at a low speed, only slight centrifugal forces are generated so that the vane pump only delivers a small amount. In the known vane pumps, a housing end wall is provided with an annular groove extending over part of the circumference of the rotor, which groove is supplied with compressed medium by another delivery pump that forms a joint pump assembly together with the vane pump. The annular groove communicates with the radially inner regions in the grooves of the rotor that are delimited by the wings. In addition to the centrifugal force, the increased pressure in the inner regions of the grooves pushes the wings radially outward toward the circumference wall. But this measure is only possible if the additional delivery pump is provided. Furthermore, the annular groove extending over only a part of the circumference of the rotor is only able to exert pressure on the inner regions over a corresponding part of a rotation of the rotor, as a result of which under some circumstances, there is only a slight contact force of the wings against the circumferential wall.